The present invention relates to an improvement in the intake manifold structure for any two- or four-stroke internal combustion engine having an even number of cylinders above four. Among the engines on which this manifold structure can be mounted are typical V-8 engines, each such engine having two banks of cylinders, one disposed on the left and one on the right. An intake manifold for distributing charges of fuel and air or of air alone among the respective cylinders is interposed between the left and right cylinder banks.
Engine performance can be enhanced by using a manifold in which the resistance to fluid flow therewithin is minimized and in which the inertia of the intake air is utilized to advantage. Resistance to fluid flow varies with the cross-sectional flow area and length of each passageway within the manifold connecting the air inlet thereof to an individual cylinder of the engine. Fluid flow resistance is also dependent upon any changes in cross-sectional area along the passageway. The inertia of the intake air gives rise to flow pulses caused by pressure waves bouncing off of just-closed air intake valves. In good manifold design, the flow pulses are minimized and even used to help pressurize the flow entering yet-to-be-charged cylinders as they are being fed sequentially in the firing order.
In addition, the need for a manifold capable of providing a uniform distribution of fluid flow to all engine cylinders has long been recognized. Uneven filling of cylinders with their respective charges of fuel and air or of air alone results in each cylinder not doing the same of work. An attempt solving this problem is found in U.S. Pat. No. 2,163,040, where, as early as 1939, Jacoby provided a manifold for a four cylinder engine.
Aldrich and Sawruk, in U.S. Pat. No. 4,119,067, which issued in 1978, improved upon Jacoby's combination by centrally locating the carburetor on a four cylinder engine between its second and third cylinders.
Vorum, in U.S. Pat. No. 4,760,819, which issued in 1988, disclosed a manifold on which the carburetor is symmetrically positioned with respect to the cylinders of a four-cylinder engine. Vorum also realized that an intake manifold can be divided into sets of primary and secondary runners for use on such an engine.
Oda et al., in U.S. Pat. No. 5,012,771, issued in 1991, realized the advantages of having a manifold for a four-stroke engine wherein the manifold has-two groups of discrete intake passages connected to two groups of cylinders which in each and the same-group are not intended to be fired one after another, respectively.
With respect to pioneering work outside of the patent literature, Edlebrock, beginning in 1938, sought to minimize the effects of the same portion of the manifold simultaneously feeding charges to two cylinders of a V-8 engine. However, Edelbrock's manifolds, including his dual layer models, allow for a substantial amount of interference to occur between charges fed into even those pairs of cylinders most separated from each other in the firing sequence. In his combinations, these pairs of cylinders are fluidly connected in such a way that a charge must be fed every 180 degrees of crankshaft revolution through a passageway shared in common by the cylinders and located immediately upstream of the flow channel serving each cylinder individually.
Similarly, until now, improved manifolds for six cylinder engines have still allowed two or more cylinders to be open simultaneously to the intake side of the engine, in a configuration in which the cylinders are fluidly connected to a passageway which they share in common and which is so located immediately upstream relative to the individual cylinders. Prior art improvements in manifolds for six cylinder engines have been directed towards increasing the length of the interval separating the flow of charges to cylinders which are fluidly interconnected in groups of threes rather than in the optimum groups of twos.
The state-of-the-art with respect to various manifolds for six cylinder engines can be appreciated by comparing the exact number of degrees of crankshaft revolution during which two or more cylinders are open, hereinafter referred to as the "simultaneously-open valves interval." For a given engine, this interval is determined by subtracting the number of degrees of crankshaft revolution during which charge passes through the first passageway which two or more cylinders share in common located upstream of their individual fluid flow channels, this number of degrees being hereinafter referred to as the "first common upstream section pulse interval", from the total number of degrees of crankshaft revolution during which any one cylinder remains open, hereinafter referred to as the "open valve duration". In a typical racing engine, the "open valve duration" is roughly 300 degrees.
Manifolds six-cylinder engines in which one flow channel at the air inlet branches into six runners, each runner being fluidly connected to one of the cylinders, have a "first common upstream section pulse interval" of 120 degrees. The "simultaneously-open valves interval" for two intake valves with such a manifold is then 180 degrees of crankshaft revolution. During this 180 degree interval, three intake valves will be open simultaneously 60 degrees, the valves being in varying states of travel.
Alternately, more advanced manifolds for six-cylinder engines according to the prior art have one flow channel at the air inlet branching into two transfer sections, each section feeding a bank of the engine and branching into three runners, each runner being fluidly connected to one of the cylinders. Such manifolds have a "first common upstream section pulse interval" or pulse interval of each bank of 240 degrees. With such a manifold, the "simultaneously-open valves interval" is reduced to 60 degrees (still substantially greater than 0 degrees), during which two intake valves are open simultaneously, of each crankshaft revolution.
In general, for engines having six or more cylinders, the prior art has failed to solve those problems which are caused by having two or more cylinders open simultaneously in a manifold configuration in which these cylinders are fed by a flow passageway they share in common located immediately upstream of those flow channels serving the individual cylinders, respectively.